This proposal is designed to test hypotheses that 1) intraluminal bile salt composition, 2) dietary fatty acid composition, and 3) genetic variations affect cholesterol absorption and cholesterol synthesis. Pilot studies were performed to evaluate feasibility of the experimental approach on 2 subjects which have been completed. Biliary bile acid composition was altered as expected with ursodeoxycholic acid treatment and expected effects on cholesterol absorption and synthesis observed. NIH funding for this subproject of a Program Project Grant is now available, and enrollment of subjects and utilization will begin in the next grant year. Very extensive use of the GCRC and especially dietary support will be essential to completion of this project.